1. Field of the Invention
The present invention relates to a capacitor in which at least one or more pairs of opposed electrodes are formed so as to interpolate a gap therebetween on the surfaces of a capacitor element made of a dielectric substance or the like, and a method of manufacturing the same.
2. Description of the Related Art
A capacitor having a pair of opposed electrodes formed so as to interpolate a gap on the surfaces of a dielectric substance is disclosed, for example, in the Japanese Patent Application Laid Open no. 3-232211. FIG. 12 and FIG. 13 illustrate this example. Such a conventional capacitor is formed such that a ceramic dielectric substance 1 of a cylindrical shape or the like is provided with a pair of electrodes 2, 2 on both the sides of a gap 3 formed on the center of the circumference thereof. The gap 3 and the electrodes 2, 2 are formed all along the circumference of the dielectric substance 1, and the electrodes 2, 2 are separated completely by the gap 3. Further, in the example of FIG. 12, an insulating coating 1 made of a resin or the like overlies a part near the edges of the electrodes 2, 2 as to oppose with the gap 3 interpolated therebetween. The electrodes 2, 2 on both the end parts of the dielectric substance 11 are exposed as the terminal parts from the insulating coating 4, however, these terminal parts can be overlaid with the other conductor layers, or can be engaged with conductor caps.
Next, the method of manufacturing this type of capacitor will be described. First, a cylindrical capacitor element 1 of a dielectric substance is prepared, on the whole surface of which a conductor film is overlain. This conductor film is formed such that a conductor paste is applied on the surface of the capacitor element 1 and baked, or the conductor film is made by plating. Next, this conductor film is trimmed by the laser trimming, and a narrow gap 3 is formed along the whole circumference of the capacitor element 1. Thereby, the conductor film is separated into a pair of the electrodes 2, 2. FIG. 13 illustrates a state thus separated. Thereafter, the insulating coating 4 and the like are formed as needed, thus producing a capacitor as shown in FIG. 12.
Further, another method of forming the electrodes 12, 12 is adopted, in which both the ends of the capacitor element 1 are soaked into the conductive paste so as not to soak the part of the gap 13 therein, and the capacitor element 1 having the conductive paste applied is baked to form the electrodes.
In the former method of manufacturing a capacitor, the conductor film formed on the surface of the capacitor element 1 has to be removed with a high preciseness by the laser trimming on the center along the whole circumference. In performing this, it is necessary to hold and rotate a small chip capacitor element 1, which needs an additional man-hour on the process.
Further, in the latter method of manufacturing a capacitor, due to the dispersion of the dimension of the capacitor element 1 or the dispersion of the soaking depth when the capacitor element 1 is soaked into the conductive paste or the like, the dimension of the gap 3 is dispersed, which does not give a high preciseness to the dimension. In this type of capacitor, the part of the gap 3 where the electrodes 2, 2 are opposed makes a capacitance, and if the dimension accuracy of the gap 3 is insufficient, the accuracy of the capacitance becomes also insufficient which is an important characteristic value for a capacitor.
Further, the foregoing insulating coating 4 is formed such that a resin is applied usually by the roll coating method and is hardened. However, due to the surface tension of the applied resin, the center part of the resin swells, and the resin is hardened as it is. Therefore, the center part of the insulating coating 4 swells in thickness, which makes the outer shape of the capacitor into the so-called barrel shape. Accordingly, when mounting the capacitor on a circuit board and soldering the electrodes 2, 2 of both the ends of the capacitor on land electrodes on the circuit bord, defective solderings are apt to be created such that the electrodes 2, 2 are placed afloat from the land electrodes to cause both the electrodes 2, 2 not to be soldered, and one of the electrodes 2, 2 is not soldered to make the one electrode 2 face upward.